1. Field of the Invention
The invention is directed to a screw press having a drive with at least one spindle nut which is vertically adjustable at a threaded spindle and to which is fastened an upper press part, a ram or the like.
2. Detailed Description of the Prior Art
Along with hydraulic presses, mechanical screw presses are widely used and are known in a great variety of constructional forms. The operating principle of the screw press has remained unchanged over the ages. A screw or threaded spindle which is usually arranged perpendicular to a press table is set in rotation by a drive, thereby raising a spindle nut that can be fixed in relation to the press table in a variety of ways. DE 201 08 706 U1 discloses a screw press in which a ram is fixed to a housing-fixed spindle nut. In this embodiment form, the tubular ram in coaxial arrangement overlaps a free end of the threaded spindle which, at the other end above a press table, is set in rotation by an electric drive.
Other constructional forms of screw presses are described in DE 20 2005 013 002 U1, DE 20 2011 004 317 U1 and DE 20 2011 002 788 U1. In these generic screw presses, an upper press part is moved relative to a press table. Because a process of this kind must be carried out in a very exact manner, e.g. four drive-independent column-like guides are provided in these screw presses between the press table and the upper press part. The drive of at least two, usually four, threaded spindles is arranged in or under the press table. The spindle nuts which are vertically adjustable on the threaded spindles are fixed to the upper press part, and the threaded rods penetrate the upper press part at a slight height thereof above the press table.
In presses of this kind having an upper press part moving along guides, a further problem consists in accurately identifying the pressing force during a pressing process.
When a load cell which senses the threaded spindle coaxially and provides exact values is provided between the spindle nuts in the screw press according to DE 201 08 706 U1, transducers are arranged in or on the press table in the generic presses under discussion; the readings of these transducers have limited meaning when the press table is loaded asymmetrically.